Since the birth of the first integrated circuit, the technology of the integrated circuit has been developing following the Moore's law all the time. The semiconductor device has been sized down continuously. Meanwhile, because a sub-threshold slope of the conventional MOSFET cannot be decreased simultaneously with the shrink of the device due to the limitation of the thermoelectric force kT/q, a leakage current of the device increases, and thus the power consumption of the entire chip constantly rises, increasing the power consumption density of the chip sharply and thus severely blocking the chip from being applied to the system integration. In order to adapt to the developing trend of the integrated circuits, it is very important to research and develop a novel device having ultra-low power consumption. A tunneling field effect transistor (TFET) uses a new operation mechanism, namely, a band-to-band tunneling (BTBT), and has become a new and promising device for low power system integration application. The TFET modulates the energy band of the channel via its gate electrode, so that electrons in the valence band at the source terminal tunnel to the conduction band at the channel (or the electrons in the valence band at the channel tunnel to the conduction band at the source terminal) to form a tunneling current. Such a new operation mechanism breaks through the limitation of the thermoelectric potential kT/q in a sub-threshold slope theory limit of the conventional MOSFET, and can achieve an ultra steep sub-threshold slope lower than 60 mV/dec, reducing a static state leakage current of the device and thus reducing the static power consumption of the device.
However, an output characteristic of the TFET is entirely different from that of the conventional MOSFET. In the output characteristic of the conventional MOSFET, is achieved by an increase of a carrier mobility caused by the drain voltage. In the TFET, however, the increase of the output current with the increase of the drain voltage is achieved through the effective modulation of the tunneling width in the tunneling junction by the drain voltage, which is mainly dropped at the tunneling junction. Since there is an exponential relationship between the output tunneling current value and the tunneling width λ, the drain voltage and the output tunneling current exhibit a super-exponential relationship. Therefore, an unsaturation region in the forepart of the output characteristic curve of the TFET becomes a nonlinear super exponential characteristic curve, that is, an output resistance of the transistor being applied to circuits is very large. Such an output characteristic of the TFET is detrimental to its application to circuits, and thus to improve the output characteristic of the TFET is an important issue in the application of the TFET to circuits.